Multimode counting device

ABSTRACT

A multimode counting device that utilizes number incrementing and number decrementing signals to change the value of a stored number. The counting device includes a storage register and switching or gating circuitry that causes the device to switch between a first mode of operation for altering a stored number having a positive polarity and a second mode of operation for altering a stored number having a negative polarity. The device also includes additional gating circuitry responsive to the stored number and to signals in transmission to the storage register to initiate a change in the operating mode when the stored number is unity and a signal that will cause that number to become zero is in transmission to that register instead of waiting until the stored number actually reaches zero.

MULTIMODE COUNTING DEVICE BACKGROUND OF THE INVENTION l. Field of theInvention Electronic counting devices.

2. Brief Description of the Prior Art Multimode counting devices areknown. Any device capable of utilizing number incrementing and numberdecrementing signals to change the value of a stored number that canhave either a positive or a negative polarity must be constructed tooperate in two modes. That is, a number incrementing signal or signalthat will cause the actual value of the stored number to be increasedmust increase the magnitude, or absolute value of the stored number whenthe stored number has a positive polarity, but it must decrease themagnitude of the stored number when that number has a negative polarity.Similarly,'a number decrementing signal, or signal that decreases theactual value of the stored number, must decrease the magnitude of thatnumber when the stored number has a positive polarity, but it mustincrease the magnitude of that number when the stored number has anegative polarity.

Conventional multimode counting devices include a storage register,means for transmitting number chang ing signals to the storage register,and means for switching the operation of the counting device from onemode to another. The storage register is constructed to provide anoutput indicating the value of the stored number. When the value of thestored number is zero, the storage register provides an output thatenables the mode switching means to respond to the next number changingsignal received by the counting device and change the operating mode ofthe device accordingly. If this next received number changing signal isa number incrementing signal, the stored number will have a positivepolarity, and the mode determining apparatus provides an output thatwill cause the counting device to operate in a first mode for changingpositive polarity numbers. Similarly, if this next received numberchanging signal is a number decrementing signal, the stored number willhave a negative polarity and the mode determining apparatus provides anoutput that will cause the counting device to operate in a second modefor changing negative polarity numbers.

In designing a counting and number storing device, it is desirable tomaximize the rate at which the device can receive number changingsignals. The rate at which signals can be received by theabove-described device is limited by the fact that a first signal mustpropagate to the storage register, the value of the number stored in thestorage register must be changed in response to this received numberchanging signal, the storage register must produce an output indicatingthe value of the stored number, and this output must propagate to andenable or activate the mode switching means, before a second numberchanging signal can be received by the counting and number storingdevice. lf signals are received at a faster rate, the mode determiningmeans would not be ready to respond to the signal received by thecounting device immediately following the number changing signal thatcauses the value of the stored number to be zero and an error willoccur.

SUMMARY oF THE INVENTION The subject invention comprises a counting andnumber storing device that can receive number changing signals at afaster rate than can the prior art counters because it is constructed toproduce a signal that enables mode determining means to switch the modeof operation at a time when it is known that the stored number will havea zero value, but before that zero value is actually obtained. Inaddition to mode determining means, the device includes number storingmeans, means for receiving number changing signals and transmittingthose signals to the number storing means, and means for providing acount direction signal that indicates whether a number changing signalin transmission to the number storing means will cause the magnitude ofthe stored number to be incremented or decremented.

The number storing means includes gating means responsive to the valueof the stored number and the count direction signals for providing anoutput signal that enables the mode determining means to change theoperating mode of the counting and number storing device. The gatingmeans is also connected to receive number changing signals intransmission to the number storing means. An enabling signal output isprovided when the gating means receives signals indicating that themagnitude of the stored number is unity and that the next numberchanging signal to be received by the number storing means willdecrement the magnitude of the stored number. This enabling signalallows the mode determining means to receive and respond to the nextnumber changing signal received by the counting and number storingdevice. Since the number changing signal that will cause the magnitudeof the stored number to be zero is the signal that caused the enablingsignal to be transmitted to the mode determining means, this next numberchanging signal received by the device will be the signal that willchange the magnitude of the stored number from zero to either plus orminus unity. The mode determining means receives and responds to thissignal, and provides an output that will cause the device to operate ina first mode for changing a positive polarity number if it is a numberincrementing signal, and provides an output that will cause the deviceto operate in a second mode for changing a negative polarity number ifit is a number decrementing signal.

Since an enabling signal is provided to the mode determining meansbefore the value of the stored number reaches zero, number changingsignals can be received by the counting device of this invention at afaster rate than they can be received by the prior art counting devices.There is no need for a first number changing signal to be received bythe number storing means and change the value of that stored numberbefore a second number changing signal can be received by the subjectcounting and number storing device. It is only necessary to determinethat a number changing signal has been received by the counting andnumber storing device that will cause the stored number to have a zerovalue when the number storing means of this device receive and respondto that signal.

To insure that the number changing signal received and used by theenabled mode determining means to determine the operating mode of thecounting device is actually the number changing signal that will changethe value of the stored number from zero, the gating means fortransmitting an enabling signal to the mode determining means isconnected to receive number changing signals being transmitted to thenumber storing means at a point downstream from the point at which themode determining means receives those signals. The gating means isconstructed to provide an enabling signal only when the number changingsignal that will cause the stored number to have a zero value passesthis downstream position. This prevents the premature transmission of anenabling signal to the mode determining means that would allow the modedetermining means to receive the number changing signal that will causethe stored number to have a zero value instead of the number changingsignal that will cause the stored number t change from zero to eitherplus or minus unity.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects, features andadvantages of this invention, which is defined by the appended claims,will become apparent from a consideration of the following description,and the accompanying drawing in which:

The FIGURE is a circuit diagram of one embodiment of the multimodecounting and number storing device in this invention.

DETAILED DESCRIPTION OF THE DRAWING The FIGURE illustrates a multimodecounting and number storing device 10 that includes number storing means12, means 14 for receiving number changing signals and for transmittingthose signals to the number storing means 12, and means 16 fordetermining the operating mode of the device 10. The device 10 alsoincludes gating and storing means 18 that provide count directionsignals that indicate whether each number changing signal intransmission to the number storing means 12 will increment or decrementthe magnitude of the stored number.

The number storing means l2 includes four conventional decade storageregisters 20, 22, 24, and 26. Each register is constructed to store adecimal digit of value 0-9 in a binary code form. Each register includesa ter minal labelled CK for receiving signals hereinafter referred to asclock signals. The value of the digit stored in a register is changed byeach clock signal received by that register. All clock signalstransmitted to the registers 20-26 are identical. The direction in whicha stored digit is changed is determined by a count direction signaltransmitted to the storage registers along line 28 and received by thoseregisters at terminals labelled MC. Gating and storing means 18 provideseither a first or a second count direction signal, depending on thenature of the number changing signal received by the device 10 and thepolarity of the stored number. A rst count direction signal will causethe value of the stored digit to be increased by the next received clocksignal. A second count direction signal will cause the number stored bya decimal register to be decreased upon the receipt of the next clocksignal. lt is a characteristic of the decade registers 20-26 that acount direction signal must be received a predetermined amount of timebefore a clock signal in order to qualify those registers to respond tothe clock signal in a proper manner.

Registers 20, 22, 24, and 26 stored progressively more significantdigits. That is, the least significant digit is stored in register 20,which is thus constructed to receive each clock signal transmitted tothe storing means 12. Signals transmitted along line 30 to the storingmeans 12 are placed in proper form for reception by register 20 by aninverter 32. Registers 22, 24, and 26 do not receive every clock signaltransmitted to the number storing apparatus since they store moresignificant digits. AND gates 34, 36, and 38 control the transmission ofa clock signal to these registers. Each of these AND gates will transmita signal to its associated decade register only upon the receipt of aclock signal and signals from the terminals labelled U/D of eachregister storing a less significant digit.

Each register includes gating means responsive to the value of thestored digit and to the count direction signals for controlling thetransmission of signals from the U/D terminal. An output signal isprovided from the U/D terminal of a register only when the digit 9 isstored in that register and a count direction signal is received thatwill cause the next clock signal to increment the value of the storednumber, and when the digit 0 is stored in that register and a countdirection signal is received that will cause the next clock signal todecrement the value of the stored number.

A gate such as gate 36 controlling the transmission of clock signals tothe register 24 will transmit a clock signal to that register only uponthe receipt of a clock signal and output signals from the U/D terminalregisters 20 and 22. This insures that a clock signal will change onlythe appropriate digits of a stored number. For example, suppose themagnitude of the stored number were 2,798 with the digits 2, 7, 9, and 8stored in the registers 26, 24, 22, and 20, respectively. The receipt ofa count direction signal directing the magnitude of the stored number tobe increased and a clock signal would change only the digit in register20 and change the magnitude of the stored number to 2,799. However, thereceipt of another count direction signal directing the magnitude of thestored number to be increased would cause registers 20 and 22 to provideoutput signals from their U/D terminals and qualify gates 34 and 36,respectively, so that the next clock signal would change the digitsstored in registers 20, 22, and 24 to give the stored number a magnitudeof 2,800. Similarly, if the stored number had a magnitude of 1,901, anda count direction signal directing the magnitude of the stored number tobe decreased were received, the next clock signal would change only thevalue of the digit in register 20 to give the stored number a magnitudeof 1,900. However, another signal directing the magnitude to bedecreased would cause registers 20 and 22 to provide output signals fromtheir U/D terminals to gates 34 and 36 so that the next clock signalwould change the digits stored'in registers 20, 22, and 24 and give thestored number a magnitude of 1,899.

In addition to qualifying gates 3438, the output signals from the U/Dterminals of decimal registers 22, 24, and 26 are transmitted to agating means 40 along lines 42, 44, and 46, respectively. The binarysignals representing the digits stored in register 20 are transmitted toa One Detector 50 which is a known gating device responsive to thebinary code of the stored digit and designed to provide an output signalalong line 48 only when the digit stored in register 20 has a magnitudeof unity. Gating means 40 thus receives signals along lines 42, 44, 46,and 48 when themag nitude of the stored number is unity and a countdirection signal has been received by the storage registers 20, 22, 24,and 26 that directs those registers to decrease the magnitude of thestored number in response to the next received clock signal. Gatingmeans 40 provides an output along line 52 only when signals are receivedon lines 42, 44, 46, 48, and 54, but no signal is received along line56. The receipt of a signal along line 54 and lack os a signal alongline 56 indicates that a clock signal is in transmission to the decimalstorage registers and that it has passed a predetermined point 58 in itstravel to those registers. Gating means 40 thus provides an outputsignal when it is determined that a clock signal is in transmission tothe storage registers 20-46 that will cause the magnitude of the storednumber to be zero, but before the stored number actually obtains thatzero value.

The output signal from gating means 40 is transmitted to a flip-flop 60which also receives clock signals along line 62. Flip-flop 60 providesan output that enables the mode determining apparatus 16 to respond tonumber changing signals received by the device and change the mode ofoperation of that device if appropriate.

It is noted that gating means 40 could also provide an output signalalong line 52 when the stored number has a magnitude of 9991 and a countdirection signal that directs the magnitude of the stored number beincreased by the next clock signal is received by the registers -26. Butsince this value is at the extreme of the count range, it can beconsidered an illegal state and ignored. It would be an obvious matterfor one skilled in this art to design count registers in which the U/Dterminals of the illustrated registers are replaced by two outputterminals, a first for providing signals which qualify gates controllingthe transmission of clock signals to registers containing moresignificant digits, and a second for providing output signals to gatingmeans 40. An output signal would be transmitted from this secondterminal only when the magnitude of the stored digit is zero and a countdirection signal is received that directs the magnitude of the storeddigit to be decremented by the next received clock signal. This modifieddesign would thus eliminate the transmission of an erroneous signal fromgating means 40 when the magnitude of the stored number reaches 9991.However, it would only extend the range of the counting device to 9999.Since this range extension is so slight, the illustrated decade storageregisters are used in thepreferred embodiment of this invention becausethey are commercially available and can be obtained at less cost thancan the above-described modified registers.

The mode determining apparatus 16 receives number changing signals fromlines 64 and 66 of the receiving and transmitting apparatus 14, andresponds to these signals upon the receipt of an appropriate enablingsignal from flip-flop 60. As has been described above, a signal istransmitted to the mode determining means 16 which enables those meansto respond to the first number changing signal received by the device 10after it receives a number changing signal that will cause the storednumber to have a value of zero. This signal following the zero causingsignal will cause the value of the stored number to have a value ofeither plus or minus unity. lf it is a number incrementing signal whichwill give the stored number a positive polarity, the mode determiningmeans responds to this signal by providing an output to gating means 18that will cause the device 10 to operate in a first mode for changing apositive polarity number. Similarly, if the number changing signalfollowing the zero causing signal is a number decrementng signal whichwill thus give the stored number a negative polarity, mode determiningmeans 16 provides an output to gating means 18 that causes the device 10to operate in a second mode for changing a negative polarity number.

In order to provide operation in the proper mode, AND gate 68 producesan output only upon receipt of a number changing signal and an enablingsignal from flip-flop 60. AND gate 68 provides a high output along line70 and a low output along line 72 upon receipt of a signal fromflip-flop 60 and a number incrementing signal. It provides a low outputalong line 70 and a high output along line 72 upon receipt of a signalfrom flipflop 60 and a number decrementng signal. The outputs from ANDgate 68 are transmitted to a sign flip-flop 74. This flip-flop providesa high output along line 76 and a low output along line 78 in responseto the receipt of a high output along line 70. It will continue toprovide these outputs along lines 76 and 78 until a high signal isreceived along line 72 and a low signal is received along line 70,whereupon it will provide a low output along line 76 and high outputalong line 78. This output state will also be maintained by flip-flop 74until further signals switching its output state are received.

The signals transmitted along lines 76 and 78 determine the nature ofthe count direction signal produced by gating means 18. Gating means 18is constructed to provide first count direction signals that cause themagnitude of the stored number to be incremented, and second countdirection signals that cause the magnitude of the stored number to bedecremented. The particular output signal provided by gating means 18 isdetermined by the number changing and count direction signals receivedby gating means 18. Gating means 18 stores received signals, provides anoutput determined by the signals received, and continues to provide thatoutput until it receives either a subsequent count direction signal or asubsequent number changing signal that will cause the output of gatingmeans 18 to be changed. When gating means 18 receives a high signalalong line 76, it provides a rst count direction signal in response toeach number incrementing signal it receives and a second count directionsignal in response to each number decrementng signal it receives. A highsignal received along line 76 thus causes gating means 18 to operate ina first mode for changing the magnitude of a positive polarity number.When gating means 18 receives a high signal along line 78, it isconstructed to provide a second count direction signal in response toeach number incrementing signal it receives and a first count directionsignal in response to each number decrementng signal it receives. A highsignal transmitted along line 78 thus causes the gating means to operatein a second mode for changing the magnitude of a negative polaritynumber.

Number incrementing and number decrementing signals are received by thecounting and nhumber storing device l along lines 64 and 66,respectively. These signals are received by the transmitting apparatus14 which generates a clock signal for each received number incrementingand number decrementing signal. The receiving and transmitting apparatus14 includes delays 80 and 82 for receiving number incrementing andnumber decrementing signals, respectively. These delay devices delay thetransmission of number changing signals to the gating means 18sufficiently so that the mode determining means 16 will have time toreceive each number changing signal and change the operating mode of thedevice l0 in the appropriate case before the number changing signalcausing the mode shift is received by the gating means 18. Delays 80 and82 thus prevent the production of an erroneous count directionindicating signal for the number changing signal that causes the deviceto shift from one mode of operation to another. Signals from the delaydevice 80 and 82 are transmitted to an OR gate 84. OR gate 84 providesan output signal upon receipt of a signal from either delay 80 or delay82. The output signals from OR gate 84 are all identical and will bereferred to hereinafter as clock signals. The clock signal generated fora number incrementing signal is indistinguishable from that generatedfor a number decrementing signal.

Clock signals are transmitted from OR gate 84 to delays 86 and 88. Incombination, these delays delay the transmission of a clock signal toallow sufficient time for the storage registers 20-26 to receive andrespond to the count direction signal associated with the clock signalbeing delayed so that the clock signal will change the magnitude of thestored number in the appropriate direction upon receipt of the delayedclock signal. Delays 86 and 88 also delay the transmission of a clocksignal sufficiently so that gating means 40 will receive a clock signalalong line 56 and the signals from the registers 20 to 26 that indicatethe state the storage registers will have upon receipt of that clocksignal at substantially the same time. This insures that no clock signalother than the signal that will actually cause the stored number to havea value of unity can qualify gating means 40 and cause the transmissionof an enabling signal to the mode determining means 16.

In order to prevent a long number changing signal from providing anenabling signal and then gating itself rather than the next followingnumber changing signal into the mode determining means, it is necessaryto determine that the zero causing clock signal has propagated past thepoint at which the mode deterrnining means 16 receives number changingsignals, before transmitting an enabling signal to those modedetermining means. Gating means 40 thus only provides an `output signalalong line 52 when a clock signal is received along line 54, but nosignal is received along line 56. Delay 88 separates the leading andtrailing edges of a clock signal so that a signal will be received bygating means 40 along line 56 for a sufficient time during which nosignal is received along line 54 to allow gating means 40 to respond tothat condition.

In operation, the counting and number storing device 10 receives numberincrementing and number decrementing signals along lines 64 and 66respectively. The receiving and transmitting apparatus 14 produces anidentical clock signal for each received number changing signal. Eachnumber changing signal is transmitted to the gating means 18 whichproduces a count direction signal in accordance with the nature of thenumber changing signal and the polarity of the stored number. A countdirection signal determines whether its associated clock signal willincrement or decrement the magnitude of the stored number. Both thecount direction signal and its associated clock signal are transmittedto the number storing means 1,2. The clock signal is delayed intransmission to allow sufficient time for the number storing means 12 toreceive and respond to the count direction signal so that the magnitudeof the stored number will be changed in the appropriate direction by theclock signal.

Gating means 40 provides an output when it is determined that the storednumber has a magnitude of unity and a clock signal is in transmission tothe storage registers 20-26 of the number storing means 12 that willcause the stored number to be zero. That is, storage registers 20-26provide signal outputs to the gating means 40 along lines 42-48 when themagnitude of the stored number is unity, and when a count directionsignal is received that will cause the registers to decrement themagnitude of the stored number upon receipt of the next clock signal.Gating means 40 also receives clock signals being transmitted to thenumber storing means 12. The transmission of clock signals to gatingmeans 40 is delayed sufficiently so that the clock signal to be nextreceived by the storage registers 20-26 is received by the gating means40 along line 54 at substantially the same time that gating means 40receives signals indicating the magnitude of the stored number and thedirection the magnitude will be changed by the next received clocksignal. Gating means 40 provide an output signal along line 52 whensignals are received along lines 42-48 and 54, and no signal is receivedalong line 56.

The clock signal that will cause the stored number to have a value ofzero causes gating means 40 to provide an output signal that enables themode determining means 16 to respond to the next number changing signalreceived by the device 10. This next signal is the signal that willchange the value of the stored number from zero to either plus or minusunity. This signal, therefore, determines the polarity of the storednumber and the operating mode of the device 10. To provide a change inthe operating mode, the output from gating means 40 is transmitted toflip-flop 60 which transmits an enabling signal to AND gate 68 uponreceipt of this signal and a clock signal along line 62. AND gate 68 incooperation with flip-flop 74 determines the operating mode of thedevice 10. AND gate 68 provides an output only in response to thereceipt of both a number changing signal and an enabling signal fromflip-flop 60. Number changing signals can, therefore, be received by thedevice 10 at a rate selected so that an enabling signal produced by onenumber changing signal will be received by AND gate 68 at substantiallythe same time that that gate receives the next number changing signal.

The counting and number storing device thus is capable of receivingnumber changing signals at a faster rate than prior art devices becausea first number changing signal need not be received by the storageregisters -26 and change the magnitude of the stored number before thesecond number can be received by the counting device as is the case withthe prior art devices. A first signal need only propagate past point 58before a second number changing signal can be received by the countingand number storing device 10, and no error in sign will be able tooccur.

Having thus described an embodiment of this invention, what is claimedis:

l. In a multimode counting and number storing system utilizing numberchanging signals to change the value of a stored number, said systemincluding:

number storing means, said number storing means providing magnitudesignals indicating the magnitude of the stored number;

means for transmitting number changing signals to said number storingmeans; means for generating a count direction signal that indicateswhether a number changing signal in transmission to said number storingmeans will cause the magnitude of said stored number to be incrementedor decremented; mode determining means for switching the mode ofoperation of said system between a first mode for altering a positivepolarity number, and a second mode for altering a negative polaritynumber, the improvement comprising:

enabling means responsive to said count direction signal and saidmagnitude signal for providing an output signal that enables said modedetermining means to switch the operating mode of said system upon thereceipt of signals indicating that said stored number has a magnitude ofunity and that a signal that will cause said stored number to have avalue of zero is in transmission to said number storing means, a changein the operating mode thereby being initiated at a time when it isdetermined that said stored number will have a value of zero, and beforethe stored number actually obtains said zero value.

2. The multimode system set forth in claim 1 in which said enablingmeans comprises gating means for transmitting said enabling outputsignal to said mode determining means upon the receipt of signals bysaid enabling means indicating that the magnitude of said stored numberwill be decremented by a signal in transmission to said number storingmeans and that the magnitude of said stored number is unity.

3. The multimode system set forth in claim l in which:

said means for generating count direction signals provides a directionsignal for each number changing signal in transmission to said numberstoring means;

and in which said enabling means includes:

gating `means connected to receive said count direction signals, andsaid number changing signals; and

means for delaying the transmission of at least one of said signals tosaid gating means so that each number changing signal and its associateddirection signal will arrive at said gating means at substantially thesame time to permit only a signal that will cause the stored number tohave a zero value to cause said enabling means to transmit an enablingsignal to said mode determining means.

4. The multimode system set forth in claim 3 in which:

said enabling gating means also receives said magnitude signals; andsaid delay means delays the transmission of signals to said gating meansso that a signal indicating the magnitude of said stored number to beunity, and the number changing signal that will change the stored numberfrom unity both arrive at said gating means at substantially the sametime to prevent an erroneous transmission of an enabling signal. S. Themultimode counting and number storage device set forth in claim l inwhich:

said mode determining means receives number changing signals from saidtransmitting means and enabling signals from said enabling means, andprovides an output that causes the said system to operate when enabledby an enabling signal that is in accordance with a received numberchanging signal; said enabling means includes gating means connected toreceive signals from said transmitting means at a position downstreamfrom the position at which said mode determining means receives signalsfrom said transmitting means; and said enabling gating means transmitsan enabling sigial only when no signal is received from said downstreamposition, said enabling means thereby preventing said mode determiningmeans from responding to any number changing signal that will cause saidstored number to have a zero value and causing said system to operate ina mode determined by said zero causing signal instead by the numberchanging signal following said zero causing signal. 6. A method ofdetermining the proper counting mode for changing a stored number of aparticular polarity in response to number changing signals comprisingthe steps of:

transmitting number changing signals in a sequence to a number storingmeans constructed to change the value of the stored number in responseto said received number changing signals; generating signals indicatingthe magnitude of the stored number; generating a count direction signalfor each number changing signal in transmission to the said storingmeans that indicates whether the number changing signal will cause themagnitude of the stored number to be incremented or decremented;initiating the generation of a mode determining signal when themagnitude of the stored number is unity and a number changing signal isin transmission to said storing means that will cause the magnitude ofthe stored number to be zero; and generating said mode determiningsignal in accordance with the number changing signal immediatelyfollowing the number changing signal that will cause the value of thestored number to be zero, said mode determining signal causing countingto be performed in a first mode for altering a positive polarity numberwhen said following signal is a number incrementing signal and causingcounting to be performed in a second mode for altering a negativepolarity number when said following signal is a number decrementingsignal,

* ll #l #l

1. In a multimode counting and number storing system utilizing numberchanging signals to change the value of a stored number, said systemincluding: number storing means, said number storing means providingmagnitude signals indicating the magnitude of the stored number; meansfor transmitting number changing signals to said number storing means;means for generating a count direction signal that indicates whether anumber changing signal in transmission to said number storing means willcause the magnitude of said stored number to be incremented ordecremented; mode determining means for switching the mode of operationof said system between a first mode for altering a positive polaritynumber, and a second mode for altering a negative polarity number, theimprovement comprising: enabling means responsive to said countdirection signal and said magnitude signal for providing an outputsignal that enables said mode determining means to switch the operatingmode of said system upon the receipt of signals indicating that saidstored number has a magnitude of unity and that a signal that will causesaid stored number to have a value of zero is in transmission to saidnumber storing means, a change in the operating mode thereby beinginitiated at a time when it is determined that said stored number willhave a value of zero, and before the stored number actually obtains saidzero value.
 2. The multimode system set forth in claim 1 in which saidenabling means comprises gating means for transmitting said enablingoutput signal to said mode determining means upon the receipt of signalsby said enabling means indicating that the magnitude of said storednumber will be decremented by a signal in transmission to said numberstoring means and that the magnitude of said stored number is unity. 3.The multimode system set forth in claim 1 in which: said means forgenerating count direction signals provides a direction signal for eachnumber changing signal in transmission to said number storing means; andin which said enabling means includes: gating means connected to receivesaid count direction signals, and said number changing signals; andmeans for delaying the transmission of at least one of said signals tosaid gating means so that each number changing signal and its associateddirection signal will arrive at said gating means at substantially thesame time to permit only a signal that will cause the stored number tohave a zero value to cause said enabling means to transmit an enablingsignal to said mode determining means.
 4. The multimode system set forthin claim 3 in which: said enabling gating means also receives saidmagnitude signals; and said delay means delays the transmission ofsignals to said gating means so that a signal indicating the magnitudeof said stored number to be unity, and the number changing signal thatwill change the stored number from unity both arrive at said gatingmeans at substantIally the same time to prevent an erroneoustransmission of an enabling signal.
 5. The multimode counting and numberstorage device set forth in claim 1 in which: said mode determiningmeans receives number changing signals from said transmitting means andenabling signals from said enabling means, and provides an output thatcauses the said system to operate when enabled by an enabling signalthat is in accordance with a received number changing signal; saidenabling means includes gating means connected to receive signals fromsaid transmitting means at a position downstream from the position atwhich said mode determining means receives signals from saidtransmitting means; and said enabling gating means transmits an enablingsignal only when no signal is received from said downstream position,said enabling means thereby preventing said mode determining means fromresponding to any number changing signal that will cause said storednumber to have a zero value and causing said system to operate in a modedetermined by said zero causing signal instead by the number changingsignal following said zero causing signal.
 6. A method of determiningthe proper counting mode for changing a stored number of a particularpolarity in response to number changing signals comprising the steps of:transmitting number changing signals in a sequence to a number storingmeans constructed to change the value of the stored number in responseto said received number changing signals; generating signals indicatingthe magnitude of the stored number; generating a count direction signalfor each number changing signal in transmission to the said storingmeans that indicates whether the number changing signal will cause themagnitude of the stored number to be incremented or decremented;initiating the generation of a mode determining signal when themagnitude of the stored number is unity and a number changing signal isin transmission to said storing means that will cause the magnitude ofthe stored number to be zero; and generating said mode determiningsignal in accordance with the number changing signal immediatelyfollowing the number changing signal that will cause the value of thestored number to be zero, said mode determining signal causing countingto be performed in a first mode for altering a positive polarity numberwhen said following signal is a number incrementing signal and causingcounting to be performed in a second mode for altering a negativepolarity number when said following signal is a number decrementingsignal.